GH4098合金短时持久性能的研究

以固溶加时效处理后的GH4098合金板材为研究对象,测定其在不同温度(800~1000℃)、不同应力(90~680MPa)条件下的短时持久性能(持久断裂时间10 min~3 h),并对其显微组织和断裂特征进行表征。结果表明:GH4098合金在800~1000℃范围内持久断裂模式均为沿晶塑性断裂。随着温度的升高,GH4098合金短时持久性能逐渐降低,但在1000℃持久性能退化程度明显加剧。组织表征结果表明:GH4098合金晶粒尺寸并未随着温度的升高而变化,而高温下合金中γ’相体积分数的降低以及γ’相和晶界碳化物的粗化是合金短时持久性能显著退化的主要原因。同时,对冷却速度对合金显微组织的影响以及短时蠕变与传统蠕变的异同也进行了讨论。     

Polyacrylonitrile-based electrospun nanofibers carrying gold nanoparticles in situ formed by photochemical assembly

Polyacrylonitrile (PAN) nanofibrous fabrics carrying gold nanoparticles (AuNPs) were prepared via the combination of electrospinning of PAN solution containing HAuCl₄ and in situ gold formation induced by ultraviolet (UV) irradiation. The factors to control the diameter of AuNPs were first investigated, and then their applicability to catalytic reaction using the obtained fibers was presented. The initial contents of Au ranging from 3 to 21 wt% did not exert a significant effect on the size of AuNPs formed in/on the PAN fibers, giving 4.7–5.4 nm in diameter, for 5 days of UV irradiation. On the other hand, the sizes of formed AuNPs were found to change from 5.2 to 2.7 nm with varying UV irradiation time from 5 to 1 day. The first-order rate constants obtained for the reduction of 4-nitrophenol increased from 1.1 × 10^?3, 3.5 × 10^?3 to 4.0 × 10^?3 s^?1, under a fixed volume of the fibers with AuNPs as catalysts, with increasing content of Au from 3, 13 to 21 wt%. The PAN catalysts with decreased size of AuNPs obtained through 1 day of UV irradiation gave a higher rate constant of 2.7 × 10^?2 s^?1. The highest rate constant per Au content and turnover frequency obtained in this study were 8.3 × 10^?2 s^?1 μmol-Au^?1 and 71 h^?1, respectively.     

Development of an optical flying head for a next-generation magneto-optical recording system

We have developed an optical flying head (OFH) comprising a thin-film coil and a high numerical aperture lens for magneto-optical (MO) disk drives. Experiments have shown successful writing and reading of MO media. The following describes the design and testing of the OFH.     

Mixed convection in a horizontal square duct with local inner heating

Numerical analyses were performed for the effect of local inner heating on the mixing flow in a horizontal square duct. Three‐dimensional governing equations were solved for Re = 100,Pr = 0.72, and six kinds of inner heating sizes in a duct, with insulated walls or uniform temperature walls. Local inner heating induced the local buoyancy force and produced four recirculating flows across a section in a thermally insulated duct. In a horizontal square duct with uniform wall temperature, the interaction of the buoyancy‐induced flows by temperature difference between the fluid and the local inner heating, and between the fluid and the walls reduced the maximum intensity of the secondary flow. Two recirculating flows were generated in a downward region. Heat transfer was locally enhanced or depressed corresponding to the flow situation. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(3): 160–170, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20056     

Preparation of Transparent Thick Films by Electrophoretic Sol-Gel Deposition Using Phenyltriethoxysilane-Derived Particles

Thick films were prepared on glass substrates coated with indium tin oxide (ITO) via electrophoretic deposition using sols that contained phenylsilsesquioxane (PhSiO_3/2) particles derived from phenyltriethoxysilane. The transparency of the thick PhSiO_3/2 films was significantly improved via heat treatment at temperatures >200°C. Scanning electron microscopy observation showed that the thick films changed in morphology, from aggregates of particles with several open spaces among the particles to a monolith with no open spaces after the heat treatment. Transparent films ~3 µm thick were obtained when the films were heat-treated at a temperature of 400°C for 2 h.     

STUDY ON THE CHARACTERISTICS OF LONG TERM DISCHARGE OF A CATCHMENT

1.　INTRODUCTIONItiswellknownthatthecharacteristicsofthecatchmentdischargewillchangewithlanduse.Inthispaper,thefocusistodiscussthemodeloflong-termdischargeofcatchmentwhichincludestwokindsoflanduse:oneisforestattheupperpartofthecatchment,theotherispaddyfieldatthelowerpartofthecatchment.Therehavebeenmanytypesofmodelsproposedforrunoffanalysis.Foralongtime,tankmodelhasbeenwidelyusedfordischargeanalysis.Attheverybeginning,therewaslessphysicalmeaning.Withtheintroductionofphysicalanalysisofhydr…     

In situ hydroxyapatite crystallization for the formation of hydroxyapatite/polymer composites

In an attempt to synthesize hydroxyapatite (HAP)/polymer composites, HAP crystallization was investigated in solution in the presence of ionic synthetic polymers. The side groups of the polymers used include carboxylate, dihydrogen phosphate, sulfate, and primary amine. Spontaneous HAP precipitation and amorphous-crystalline transformation occurring in both the presence or absence of ionic polymers were studied by measuring the solution turbidity change and titrating the released protons, respectively. The rates of HAP nucleation and growth were determined from an induction period before onset of crystallization and the subsequent propagation of HAP crystallites. The added anionic and cationic polymers, were found to suppress the crystallization in a concentration-dependent manner. An exception was a concentrated poly(acrylic acid), which was precipitated by calcium ion binding to accelerate the nucleation and the growth of HAP crystallites. These results suggest that a molecular interaction is operative between the ionic polymer chains and the growing HAP crystallites. Infrared spectroscopy and X-ray diffraction analysis revealed that the HAP precipitated in the presence of ionic polymers incorporated the polymer chains in the HAP microcrystalline aggregates. Based on these findings, HAP/poly(acrylic acid) composites were prepared through in situ HAP crystallization in the presence of poly(acrylic acid). Tensile testing of the composites and electron microscopic observation of their fractured surfaces revealed that the composite prepared through this wet process was superior to that obtained by simple physical mixing with respect to the wet state mechanical properties and homogeneity in mixing. This revised version was published online in November 2006 with corrections to the Cover Date.     

Electrochemical studies of acid-promoted disproportionation of nitroxyl radical

The acid-promoted disproportionation of 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) was studied in order to elucidate the recycling process of the catalytic oxidation of alcohol by nitroxides. Potentiometry, cyclic and hydrodynamic voltammetries with a rotating disk electrode (RDE) have been used to investigate the formation of a nitrosonium cation and a hydroxylamine by disproportionation of nitroxides in acetonitrile. The addition of p-toluenesulfonic acid caused the rest potential of the TEMPO/nitrosonium cation couple to shift in a more positive direction and decreased the peak current in the cyclic voltammograms. The subsequent addition of 2,6-lutidine as a Lewis base made the rest potential and the peak current recover. These phenomena corresponded to the recycling of the catalytic process by TEMPO in a basic aprotic solution.